1. Field of the Invention
The present invention relates generally to a microdevice comprising a thin film of ferroelectric ceramic as the active actuating material and more particularly to a micromechanical sensor/actuator device having a deflectable piezoelectric (PZT) component and a fabrication process using surface micromachining techniques.
2. Description of Related Art
Microactuators such as micromechanical valves and pumps have previously been formed using thin film materials which deform in response to an applied electric field. Other micromechanical devices such as rotating members, micro motors, and microgears have also been fabricated using integrated circuit processing technology. These technologies, however, are severely limited in the amount of usable energy which can be derived from these actuation principles based on applied electrostatic forces. Much larger actuator devices have previously been formed using macro scale, bulk crystal and ceramic materials. These devices have been used in a number of micromechanical positioning applications and applications involving the production of substantially large forces in excess of one newton.
Piezoelectric thin films are attractive for MEMS (microelectromechanical system) devices such as microsensors and actuators. In MEMS devices the development of micro sensor and actuators, many microgeometry structures have been reported. These include membranes, bridges, and cantilevers which are constructed by bulk and surface micromachining techniques. In the case of the cantilever structure, many applications have been reported such as accelerometers. There are several different types of accelerometers which use cantilever beam structures, such as capacitive, piezoresistive, and piezoelectric effects. ZnO thin films have been used for micromachined piezoelectric cantilever beam accelerometer devices because of its easy deposition process. But, it is well known that PZT has much higher piezoelectric constants than ZnO, and consequently PZT thin films have been gathering much attention in the MEMS community. Recently, bulk micromachined cantilever beams using PZT thin films have been reported. However, no surface micromachined deflectable piezoelectric microdevices using PZT thin films have been reported to date.
There is a need for surface micromachined deflectable piezoelectric microdevices based on PZT thin film and for a suitable fabrication process for such microdevices.